This invention relates to an improvement in a starting motor wherein planetary gear reduction gears are associated.
Heretofore, a starting motor of this type is constructed as shown in FIG. 1. As evident from FIG. 1, a D.C. motor 1 is a mounted on a front bracket 2, and this motor 1 has an armature 3. An armature rotational shaft 4 which extends from the armature 3 forms a spur gear section 5 which operates as a sun gear on the outer peripheral surface of the front end thereof. A planetary gear 6 is engaged in mesh with and is disposed around the spur gear section 5. The planetary gear 6 is further engaged in mesh with a ring-shaped internal gear 7 which is disposed outside the planetary gear 6, thereby forming a planetary motion mechanism. The internal gear 7 is mounted on the inner peripheral surface of a yoke 8 of the D.C. motor 1 together with an intermediate bracket 9. A sleeve bearing 10 is attached to an annular space between the axial flange inside the bracket 9 (at the side of the rotational shaft 4) and the armature rotational shaft 4, thereby bearing the armature rotational shaft 4.
A supporting pin 11 which operates as an arm is rotatably mounted at the center of the respective planetary gears 6 through a bearing 14. The end of the pin 11 is fixedly secured to a clutch outer 13 as an arm wheel. This clutch outer 13 is a part component of an overrunning clutch 12 and a cam 16 is arranged on the inner peripheral surface thereof. A wedge-shaped space is formed between a clutch inner 15 which is disposed concentrically with the clutch outer 13 and the cam 16. The rotary force of the clutch outer 13 is transmitted only with respect to the unidirectional rotation to the clutch inner 15 by means of the intrusion of a rotor 17 arranged in the wedge-shaped space into the narrow direction of the rotor 17.
The clutch inner 15 is secured fixedly to an output rotational shaft 18 which is disposed on the same axis as the axis of the armature rotational shaft 4. A helical spline 19 is formed on the outer peripheral surface of the rotational shaft 18. A pinion 20 is engaged with the rotational shaft 18, and this pinion 20 is engaged with the helical spline 19. This pinion 20 is formed so that, when the rotational shaft 18 is rotated, the pinion 20 slides forwardly and hence rightwardly in FIG. 1.
The armature rotational shaft 4 extends at the front end thereof toward the central recess formed on the side surface of the clutch inner 15. A sleeve bearing 21 is mounted between the inner peripheral surface of the central recess of the clutch inner 15 and the outer peripheral surface of the front end of the rotational shaft 4, thereby supporting each other. On the other hand, a sleeve bearing 22 is engaged with the inner peripheral surface at the front end of the front bracket 2, thereby bearing and supporting the front end of the output rotational shaft 18. There are also provided a stopper 23 which stops the forward movement of the pinion and a thrust washer 24 which bears the thrust stress generated mainly at this time on the outer peripheral surface at the front end of the rotational shaft 18.
A washer 25 is engaged with the outer rear peripheral surface of the sleeve section of the pinion 20, and the engaging groove of a shifting lever 26 is formed on the periphery of the sleeve section in cooperation with the teeth side surface of the pinion 20. This shifting lever 26 is engaged with the cam at the lever section 26b above the pivotal center of the shifting lever 26. This cam is formed at the front end of a plunger 28 of an electromagnetic switch 27 which is mounted on the front bracket 2. In this manner, the lower lever section 26a of the shifting lever 26 is rotatably energized counterclockwise in FIG. 1 by the operation of the switch 27.
The operation of the conventional starting motor with the planetary gear reduction gears thus constructed will be described hereinafter.
The pinion 20 is forwardly shifted on the helical spline 19 of the output rotational shaft 18 by the energization of the electromagnetic switch 27, and is thus engaged in mesh with a ring gear (not shown) of an internal combustion engine (not shown). When the main contact (not shown) of the switch 27 is then closed and the armature 3 is energized, rotary force is generated. Thus, the planetary gear 6 is driven through the spur gear section 5 on the armataure rotational shaft 4. The rotating speed of the armature 3 is internally decelerated and is transmitted to the overrunning clutch 12. As a result, the output rotational shaft 18 is rotated in one direction through the clutch, and the pinion 20 is thereby rotated to drive the ring gear of the internal cumbustion engine, thereby starting the internal combustion engine.
Since the conventional starting motor with the planetary gear reduction gears thus constructed is, however, engaged at the pinion in mesh with the internal combustion engine which is stopped immediately before the armature is energized at the starting time, high stress is generated at the reduction gears at the time of energizing the armature. Since the reduction gears are further rotated without load after the engine is started and are thus rotated at a high speed, the reduction gears have drawbacks such as the wearing out of the reduction gears in a short time, etc.